2. DOM Inspector – Leftover from the days in web dev and stuff. See what that web page really contains.
3. Tabbrowser Preferences – Do funky things with your tabs.
4. IE Tab – Windows/office update in Firefox!
5. User Agent Switcher – "This web site is best view in IE" No problem! *Jedi hand wave* I am using IE.
6. Live HTTP Headers – Another leftover from my legacy days of grokking application and web servers. See what the server really thinks of you.